The only OSHA standards that make mention of the phrase “Double Block and Bleed” (DB&B) are its Permit-Required Confined Space (PRCS) standards. In both 1910.146(b) and 1926.1203, OSHA defines a DB&B as:
the closure of a line, duct, or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.
PLEASE take notice that OSHA requires TWO (2) in-line valves are CLOSED and the drain/vent valve in between the CLOSED valves be locked or tagged OPEN. This is in stark contrast to how one American Petroleum Institute standard defines DB&B. API 6D Specification for Pipeline Valves defines a DB&B arrangement using a SINGLE valve as:
